EP 0554581 B1 discloses a laminated magnetic core for an antenna, used for an identity card or a credit card-like card, and consisting of a stack of amorphous magnetic layers and film-like non-conducting layers arranged in between, for example, made of plastic. Flexibility is required of the antenna presented there, if it is exposed as an identity card to certain mechanical loads during daily use.
An antenna for a transponder is known from EP 0762535 B1 with a magnetic core consisting of different layers of a soft magnetic material, for example, an amorphous magnetic material with or without intermediate insulation layers in the form of paper or polymer. As an alternative, casting of strips of magnetic active material with plastics, for example, resins, is also disclosed there. The variant described there is used to create a flexible and rupture-proof antenna.
A magnetic core element for a thin film antenna is known from DE 19513607 C2, in which the magnetic core consists of strips of an amorphous alloy or a nanocrystalline alloy, which can be insulated from each other by insulation strips, in which case separation of the laminate layers by their oxide layers is also mentioned.
A stack of soft magnetic elements is also known, for example, from U.S. Pat. No. 5,567,537, in which the use of certain amorphous and nanocrystalline alloys is described for production of so-called thin film antennas. Among other things, the retention of soft magnetic or other physical properties before and after a bending load is mentioned as a criterion for good usability of such thin film antennas, for example, in chip cards. It is shown, in particular, that such thin film antennas exhibit no cracks after bending loads, in contrast to ferrite rods.
U.S. Pat. No. 5,625,366 discloses a flexible antenna core, consisting of a laminate of different layers of an amorphous alloy, in which a strand-like bundle of strand-like magnetically active elements is additionally mentioned, between which, if necessary, a film insulation can also be provided. In addition, the possibility of producing insulation of the individual elements by an oxide layer or another layer, which can be created, for example, by chemical treatment of the magnetic elements, is also mentioned.
For actually strongly deformable antennas, especially longer bulky antennas with a wire winding, the amorphous and nanocrystalline alloys already known from the cited prior art, as well as the internal structure of the antenna cores, are only suitable with considerable restriction. In vehicle access systems, only non-deformable ferrite cores have thus far been used.